Lipoprotein from the outer membrane of Escherichia coli: purification, paracrystallization, and some properties of its free form

Effect of the aggregational state on the mitogenicity of lipoprotein from the outer membrane of Escherichia coli

The effects of ultrasonication, electrodialysis, and centrifugation through sucrose gradients on the mitogenicity of the lipoprotein (LP) from the outer membrane of Escherichia coli were studied in several inbred mouse strains. LP is not readily soluble in aqueous solution. By ultrasonication for 1 minute we obtained LP aggregates which were fully mitogenic; prolonged sonification had no influence on activity. Solubilization in 4% sodium dodecyl sulphate (SDS) and centrifugation into sucrose gradients yielded different aggregation forms of LP, which were B-lymphocyte mitogens towards LPS non responder C3H/HeJ mouse splenocytes, and towards congenitally athymic nude mice. By electrodialysis, LP could be transformed into different salt forms. The TEA-salt of LP exhibited enhanced mitogenicity. The results suggest that the mitogenicity of lipoprotein is widely independent from the aggregational state in which it is offered to the cells.

Outer membrane of Pseudomonas aeruginosa: heat- 2-mercaptoethanol-modifiable proteins

A number of polyacrylamide gel systems and solubilization procedures were studied to define the number and nature of "major" polypeptide bands in the outer membrane of Pseudomonas aeruginosa. It was shown that five of the eight major outer membrane proteins were "heat modifiable" in that their mobility on sodium dodecyl sulfate-polyacrylamide gel electrophoresis was determined by the solubilization temperature. Four of these heat-modifiable proteins had characteristics similar to protein II of the Escherichia coli outer membrane. Addition of lipopolysaccharide subsequent to solubilization caused reversal of the heat modification. The other heat-modifiable protein, the porin protein F, was unusually stable to sodium dodecyl sulfate. Long periods of boiling in sodium dodecyl sulfate were required to cause conversion to the heat-modified form. This was demonstrated both with outer membrane-associated and purified lipopolysaccharide-depleted protein F. Furthermore, lipopolysaccharide treatment had no effect on the mobility of heat-modified protein F. Thus it is concluded that protein F represents a new class of heat-modifiable protein. It was further demonstrated that the electrophoretic mobility of protein F was modified by 2-mercaptoethanol and that the 2-mercaptoethanol and heat modification of mobility were independent of one another. The optimal conditions for the examination of the outer membrane proteins of P. aeruginosa by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis are discussed.

Interaction of bacteriophage T4 with reconstituted cell envelopes of Escherichia coli K-12

The interaction with bacteriophage T4 of the cell surface of Escherichia coli K-12 reconstituted from outer membrane protein O-8, lipopolysaccharide, and the lipoprotein-bearing peptidoglycan sacculus was studied. The reconstituted cell surface was active as a receptor for the phage, resulting in the contraction of the tail sheath, a morphological change in the base plate which was accompanied by the extension of short tail pins down to the cell surface and the penetration of the needle through the cell surface. However, the ejection of phage deoxyribonucleic acid did not take place. Both O-8 and lipopolysaccharide were essential for the interaction. In the reconstitution, the wild-type lipopolysaccharide could not be replaced by either heptoseless lipopolysaccharide or lipid A. The lipoprotein-bearing peptidoglycan sacculus was also found to be an active component for the phage adsorption. The sacculus most likely functioned as a basal framework on which O-8 and lipopolysaccharide assembled to form a flat sheet which is large enough to interact with individual distal ends of long tail fibers of a single phage particle.

A lipopolysaccharide-binding cell-surface protein from Salmonella minnesota. Isolation, partial characterization and occurrence in different Enterobacteriaceae

1. Protein extracts obtained from Salmonella minnesota Re mutant cells by treatment with EDTA/NaC1 solution contain a protein which exhibits high affinity to bacterial lipopolysaccharides. The isolation and partial characterization of this lipopolysaccharide-binding protein is described. 2. The protein was purified from EDTA extracts by a two-step procedure consisting of ion-exchange chromatography on CM-Sephadex and preparative polyacrylamide gel electrophoresis at pH 9.5. The yield of the total purification procedure was around 16%. 3. The resulting protein preparation was homogeneous on the basis of disc gel electrophoresis, dodecylsulfate gel electrophoresis, isoelectric focusing in polyacrylamide gel and immunoelectrophoresis. 4. The isoelectric point of the protein was found to be 10.3 at 4 degrees C. Its molecular weight determined by dodecylsulfate gel electrophoresis is 15000. Its amino acid composition is characterized by the absence of histidine and proline, a low content in tyrosine and high amounts of alanine, lysine, aspartic and glutamic acid residues, or their respective amides. 5. The lipopolysaccharide-protein association was shown to be mainly due to ionic interactions of the basic protein with negatively charged groups (probably phosphate and pyrophosphate groups) of the lipid A moiety. 6. Purified lipopolysaccharide-binding protein is immunogenic in rabbits, thus enabling the preparation of specific antiserum. 7. The protein is located at the surface of Salmonella minnesota Re mutant cells as revealed by antiserum absorption with total bacteria. Ferritin-labelling studies further demonstrated that it is evenly spread over the entire cell surface. 8. Comparative antiserum absorption studies using smooth and rough strains of Salmonella minnesota, Salmonella typhimurium, Escherichia coli, Klebsiella and Shigella revealed the presence of lipopolysaccharide-binding protein (or a serologically cross-reacting antigen) in most of the strains tested. From these results the protein can be considered as a common antigen of Enterobacteriaceae.

Homology of the gene coding for outer membrane lipoprotein within various Gram-negative bacteria

The mRNA for a major outer membrane lipoprotein from Escherichia coli was found to hybridize specifically with one of the EcoRI and one of the HindIII restriction endonuclease-generated fragments of total DNA from nine bacteria in the family Enterobacteriaceae: E. coli, Shigella dysenteriae, Salmonella typhimurium, Citrobacter freundii, Klebsiella aerogenes, Enterobacter aerogenes, Edwardsiella tarda, Serratia marcescens, and Erwinia amylovora. However, among the Enterobacteriaceae, DNA from two species of Proteus (P. mirabilis and P. morganii) did not contain any restriction endonuclease fragments that hybridized with the E. coli lipoprotein mRNA. Furthermore, no hybrid bands were detected in four other gram-negative bacteria outside the family Enterobacteriaceae: Pseudomonas aeruginosa, Acinetobacter sp. HO1-N, Caulobacter crescentus, and Myxococcus xanthus. Envelope fractions from all bacteria in the family Enterobacteriaceae tested above cross-reacted with antiserum against the purified E. coli free-form lipoprotein in the Ouchterlony immunodiffusion test. Both species of Proteus, however, gave considerably weaker precipitation lines, in comparison with the intense lines produced by the other members of the family. All of the above four bacteria outside the family Enterobacteriaceae did not cross-react with anti-E. coli lipoprotein serum. From these results, the rate of evolutionary changes in the lipoprotein gene seems to be closely related to that observed for various soluble enzymes of the Enterobacteriaceae.

Lipopolysaccharide interferes with the staining of lipoprotein on polyacrylamide gels

After electrophoresis of total membrane preparations of Escherichia coli B on sodium dodecyl sulfate polyacrylamide gels, and subsequent staining with Coomassie Brilliant blue, a band corresponding to the Braun lipoprotein fails to appear. This is in contrast to similar preparations of E. coli K-12 which do display the lipoprotein upon staining. Experiments described below indicate that failure to observe this protein in E. coli B is due to interference in the staining reaction by the lipopolysaccharide present in the membrane preparations.

An Escherichia coli mutant with an amino acid alteration within the signal sequence of outer membrane prolipoprotein

Lipoprotein has been purified from an Escherichia coli strain carrying a mutation in the structural gene for murein lipoprotein (mlpA). Amino acid analysis of the purified mutant lipoprotein indicates that the mutant lipoprotein corresponds to the uncleaved prolipoprotein with a single amino acid replacement of glycine with aspartic acid. Automated Edman degradation has established the precise location of this amino acid substitution to be at the 14th residue of the prolipoprotein. This alteration in the signal sequence of prolipoprotein results in a failure of the mutated prolipoprotein to be processed. Furthermore, the structural alteration in the mutant lipoprotein appears also to have affected its topological localization in the mutant cell. Whereas lipoprotein in the wild-type strain is exclusively located in the outer membrane of the cell envelope, the membrane-bound lipoprotein in this mutant is recovered in both the inner and outer membranes of the cell envelope. The data suggest, however, that proteolytic cleavage of prolipoprotein to form mature lipoprotein is not essential for the translocation and assembly of lipoprotein into the outer membrane.

Lipoprotein from Proteus mirabilis

The biosynthesis of a Proteus mirabilis outer membrane protein of molecular weight of approximately 7,000 was found to be relatively resistant to puromycin and rifampin, as is the case for the Escherichia coli liporotein. Furthermore, the existence of the lipoprotein in P. mirabilis was indicated by a comparison of the amino acid compositions of the purified free and bound forms of this protein with those of the E. coli free and bound lipoproteins.

Spin labeling of a cysteine residue of the Escherichia coli outer membrane lipoprotein in its membrane environment

A method was developed to attach a spin label to a specific site on the structural lipoprotein of the Escherichia coli outer membrane in situ. This method takes advantage of the fact that the outer membrane of wild-type E. coli contains few residues reactive towards sulfhydryl reagents. A mutant E. coli strain has been isolated [Suzuki, H., Nishimura, Y., Iketani, H., Campisi, J., Hirashima, A., Inouye, M. & Hirota, Y. (1976) J. Bacteriol. 127, 1494-1501] in which the second position from the carboxy terminus of the lipoprotein is changed from arginine into a cysteine residue. The membrane fraction of this mutant was treated with N-(1-oxyl-2,2,5,5-tetramethylpyrrolidinyl)maleimide in the presence of EDTA and 2-mercaptoethanol. Spin label was found to be preferentially incorporated into the lipoprotein. The spectrum of the spin-labeled membrane shows two components, both arising from spin label at the same site near the carboxy terminus. The strongly immobilized component has a maximum hyperfine splitting value of 53 G, and the weakly immobilized component, 37 G. A fraction of the lipoprotein is covalently bound to the peptidoglycan layer through its carboxy-terminal lysine; the spectrum of the isolated bound form of the lipoprotein was identical to that of the free form. When the matrix protein, the other major outer membrane protein, was removed by mutation, the spectrum of the lipoprotein was altered, suggesting that these two proteins are closely associated.

Lysozyme-promoted association of protein I molecules in the outer membrane of Escherichia coli

Incubation of whole envelopes prepared from sonically oscillated Escherichia coli K-12 cultures with lysozyme in vitro resulted in the appearance of a protein species with an apparent molecular weight double that of outer membrane protein I. Similar dimers were also detected in purified outer membranes and whole envelopes from lysozyme-induced spheroplasts of E. coli K-12. This was confirmed by two-dimensional electrophoresis in which the dimers were resolved in the second dimension to run as single polypeptides of protein I. Formation of dimers was correlated with peptidoglycan degradation, but the ability of protein I molecules to associate may vary between strains of E. coli, since dimers were found only in outer membranes from E. coli W7. We suggest that extensive degradation of peptidoglycan leads to nonspecific formation of protein I aggregates, but that these aggregates do not occur in vivo.

Amino acid replacement in a mutant lipoprotein of the Escherichia coli outer membrane

The primary structure of a mutant lipoprotein of the outer membrane of Escherichia coli was investigated. This mutant was previously described as a mutant that forms a dimer of the lipoprotein by an S-S bridge (H. Suzuki et al., J. Bacteriol. 127:1494-1501, 1976). The amino acid analysis of the mutant lipoprotein revealed that the mutant lipoprotein had an extra cysteine residue, with concomitant loss of an arginine residue. From the analysis of the mutant lipoprotein revealed that the mutant lipoprotein had an extra cysteine residue, with concomitant loss of an arginine residue. From the analysis of tryptic peptides, it was found that the arginine residue at position 57 was replaced with a cysteine residue. The amino terminal structure of the mutant lipoprotein was found to be glycerylcysteine, as in the case of the wild-type lipoprotein. The present results show that the mutation that was previously determined to map at 36.5 min on the E. coli chromosome occurred in the structure gene (lpp) for the lipoprotein. This was further confirmed by the fact that a merodiploid carrying both lpp+ and lpp produces not only the wild-type lipoprotein but also the mutant lipoprotein.

Biochemical characterization of a mutant lipoprotein of Escherichia coli

A lipoprotein mutant of E. coli K-12 has been characterized. The mutant lipoprotein was found to differ from the wild-type lipoprotein in the following respects: (i) it is present in an appreciable amount in the soluble fraction (275,000 X g supernatant); (ii) it lacks the covalently-linked diglyceride; (iii) it contains an unmodified cysteine which can be carboxymethylated in vitro; (iv) it undergoes dimerization and the dimer can be converted into monomeric form by reduction with 2-mercaptoethanol; (v) both the monomeric form and especially the dimeric form of the mutant lipoprotein migrate more slowly than the corresponding forms of wild-type lipoprotein in sodium dodecyl sulfate/urea polyacrylamide gel electrophoresis; and (vi) the mutant lipoprotein is not assembled into the murein sacculi, and this results in a greatly reduced amount of bound-form lipoprotein in the mutant. These data strongly suggest that the mutation has affected the primary structure of lipoprotein, in such a way that it is not modified normally, leading to the production of a structurally-altered lipoprotein deficient in covalently-linked lipid as well as a defective assembly of the altered lipoprotein into the rigid layer of the cell envelope.

Optical properties of an outer membrane lipoprotein from Escherichia coli

The infrared spectrum of a structural lipoprotein from the Escherichia coli outer membrane indicated the lipoprotein had an alpha-helical conformation but no sign for the existence of beta-structures. From circular dichroism spectra of the lipoprotein, the alpha-helical content of the protein was found to be as high as 88% in 0.01-0.03% sodium dodecyl sulfate in the presence of 10(-5) M Mg2+ at pH 7.1 and 23 degrees C. When sodium dodecyl sulfate concentration increased higher than 0.1%, the alpha-helical content of the lipoprotein decreased to about 57%. Divalent cations, such as Mg2+ and Mn2+, were found to increase the helical content of the lipoprotein. The high alpha-helical content of the lipoprotein was observed in a wide range of temperatures (23 to 55 degrees C). The significance of the high alpha-helical content of the lipoprotein is discussed in light of the three-dimensional molecular models of the lipoprotein proposed previously.

Ultrastructure of paracrystals of a lipoprotein from the outer membrane of Escherichia coli

The highly purified lipoprotein of the outer membrane of Escherichia coli forms paracrystals. The ultrastructures of these paracrystals were examined by electron microscopy. The needle-shaped paracrystals show several different band patterns, depending on conditions of paracrystallization. Models are presented to explain possible arrangements of the lipoprotein molecules within the paracrystals.